The proposed program will study the response of the skeletal muscle to pulse pressure waves of known characteristics (amplitude, dp/dt, frequency and mean values). The perfusion system which includes a pulse wave generator is used to perfuse the isolated gracilis muscle of dogs. The initial experiments have defined the basic vascular response to alterations in amplitude of pulse pressure over a range of mean perfusion pressures. The data suggest that one portion of the microvasculature, probably arterioles, vasoconstricts when pulse pressure is increased and another portion, possibly precapillary sphincters, vasodilates when pulse pressure increases. Subsequent work will attempt to establish the validity of this interpretation. Capillary filtraton coefficients (CFC) will reflect the capillary surface area, giving a indication of the open precapillary sphincters. Measurements of oxygen consumption will reflect the metabolic state of the muscle, one of the determinants of the vascular activity. Additionalinformation will be obtained from impedance and phase measurements. Impedance will reflect compliance and inertance as well asresistance. Phase will indicate the extent of reflection of the pulse wave, a measure of the vasoconstriction of the arterioles. The response of the muscle to the characteristics of the pulse pressure other than amplitude will be investigated.